Modern outboards have it. I would guess newer inboards have it wired in, got to be some sort of boat construction regulation.
I have an older outboard that I use with my Zodiac. It doesn’t have a kill switch but I do want to get one for it.
I would guess newer inboards have it wired in,
I had a 20 foot I/O 15 years ago that had one from the factory. Only idiots dont use them.
L